refactor(patient): extract age calculation logic to shared utility

Move age calculation logic from multiple components to a shared utility function in person model
Add age display to patient entry form and update preview component to use shared utility
Remove redundant age field from select-dob component

app/models/person.ts

@@ -1,3 +1,5 @@
+import { differenceInDays, differenceInMonths, differenceInYears, parseISO } from 'date-fns'
+
 import { type Base, genBase } from './_base'
 import type { PersonAddress } from './person-address'
 import type { PersonContact } from './person-contact'
@@ -56,3 +58,44 @@ export function parseName(person: Person): string {
 
   return fullName
 }
+
+export function calculateAge(birthDate: string | Date | undefined): string {
+  if (!birthDate) {
+    return 'Masukkan tanggal lahir'
+  }
+
+  try {
+    let dateObj: Date
+
+    if (typeof birthDate === 'string') {
+      dateObj = parseISO(birthDate)
+    } else {
+      dateObj = birthDate
+    }
+
+    const today = new Date()
+
+    // Calculate years, months, and days
+    const totalYears = differenceInYears(today, dateObj)
+
+    // Calculate remaining months after years
+    const yearsPassed = new Date(dateObj)
+    yearsPassed.setFullYear(yearsPassed.getFullYear() + totalYears)
+    const remainingMonths = differenceInMonths(today, yearsPassed)
+
+    // Calculate remaining days after years and months
+    const monthsPassed = new Date(yearsPassed)
+    monthsPassed.setMonth(monthsPassed.getMonth() + remainingMonths)
+    const remainingDays = differenceInDays(today, monthsPassed)
+
+    // Format the result
+    const parts = []
+    if (totalYears > 0) parts.push(`${totalYears} Tahun`)
+    if (remainingMonths > 0) parts.push(`${remainingMonths} Bulan`)
+    if (remainingDays > 0) parts.push(`${remainingDays} Hari`)
+
+    return parts.length > 0 ? parts.join(' ') : '0 Hari'
+  } catch {
+    return 'Masukkan tanggal lahir'
+  }
+}